Colloidal materials dispersed in aqueous- or oil-based carriers have found application in a widespread number of areas such as pharmaceutical, cosmetic, paints, inks and agriculture, just to name a few. A colloidal material is characterized by presenting particles which are approximately 10 to 1,000 nanometers in size. A dispersion, formulation or composition comprising a colloidal material is considered stable when it successfully prevents the colloid from being easily agglomerated, coalesced or rapidly settled from the liquid or semi-solid carrier where it is dispersed.
A great amount of exploration has been made to develop and create colloidal dispersions and compositions that are stable against agglomeration, coalescence and settling. Some substances or compounds have been used as colloid stabilizers, providing increased stability to colloidal compositions against aforementioned issues. The term “colloid stabilizer” as used herein is intended to encompass agents which interacts favorably with the colloid improving its overall properties so as to abolish, prevent, delay or minimize their coalescence, coagulation and precipitation.
There are several classes of commercially important inorganic and organic colloids such as silicon dioxide, titanium dioxide and oatmeal. Therefore, numerous attempts to find efficient colloidal stabilizers for these materials have been done. For instance, documents CA 575194, CA 677696, EP 0976797, U.S. Pat. No. 4,902,442, WO 2009/127256 and US 2006/102052 relate to silica colloidal compositions stabilized by ammonia, sodium/potassium hydroxide, aluminum, siliconates, hydronium and amino alcohols, respectively. Patent document WO 2009/002377 discloses a method for making a stabilized-colloidal silica which includes forming a solution by mixing the colloidal silica with a solvent and then add one stabilizer selected from siloxans, surface active agents, polysorbates and acrylic polymer-based flow-enhancing.
Colloidal iron solutions (mainly ferric hydroxide) are shown to be stabilized by dextrin, more specifically yellow dextrin from potato starch as described by document GB 1249558. Also, a combination of ammonia, monovalent inorganic acid (e.g. HCl, HBr) and water-soluble aliphatic acids (e.g. gluconic acid) is used to stabilize colloidal titanium compositions according to patent U.S. Pat. No. 2,819,176.
Document U.S. Pat. No. 4,309,454 shows that thiourea is a great stabilizer of colloidal compositions for electroless deposition, decreasing deterioration of the colloid. An interesting feature is disclosed by patent U.S. Pat. No. 5,437,858, where the colloidal material presents stabilizing properties. In this case, colloidal silver is used to stabilize hydrogen peroxide solutions.
Patent document WO 2005/097937 is related to a colloidal system called “Aphron” and demonstrates that, in order to stabilize this system, it is necessary to have two special stabilizers, referred to as primary and secondary Aphron stabilizers.
All of these instances show that providing adequate stability to colloidal systems is not an easy task and that the efficacy of the stabilizer is dependent on its nature and properties as they have to properly align with the properties of both the colloidal material and the carrier.
The stability issue in skin care formulations that comprise both aqueous and/or oil phases has always been and continues to be a challenge for the professionals in this field, and still demands innovative solutions. Since these formulations are metastable systems, stabilization generally consists in decreasing the speed of the particle aggregation phenomena which are very common in colloids, including coalescence. Another fact that contributes for the destabilization is that some colloidal materials absorb water from the formulation but, over time, this previously absorbed water is released to the formulation, causing it to “leak” and, thus, such materials do not present adequate smoothness and/or are difficult and unpleasant to spread.
An interesting approach adopted for colloidal stabilization is the use of polymers. Polymers can present both hydrophobic and hydrophilic units, thus, can interact with the water-insoluble surface of the colloid and with the aqueous-based carrier fluid. Many polymers have been proposed as stabilizers of colloidal material. However, the surfaces of colloids vary substantially and will sometimes have dramatically different affinity for a given polymer. The use of organic co-solvents in the carrier to auxiliate the dispersion of the colloid may also have a deep impact on the affinity of the polymer for any given colloidal material. Polymers are believed to adsorb to the surface of the colloidal particles, thus promoting what is called steric stabilization. Examples that apply the aforementioned approach are described in U.S. Pat. Nos. 6,245,832; 5,085,698; and 4,597,794for stabilization of pigments. Recently, copolymers have been designed to present a hydrophobic unit combined with multiple types of hydrophilic units, as disclosed in documents US 2006/0084720 and EP 1666547. Although these polymers are known as colloidal stabilizers for water-based carriers, they can be insufficient stabilizers of colloids in a composition constituted by water and organic phases. This seems to be the reason behind the fact that, to the best knowledge of the inventors, polymers/copolymers have never been so far considered as stabilizers of colloidal materials in topical formulations or skin care formulations. This may be a result of the property of polymers, which generally act as thickener agents and, therefore, do not promote a smoothing effect on the formulation. This limitation is particularly relevant when considering pharmaceutical and/or cosmetic compositions comprising higher levels of colloidal materials such as colloidal oatmeal (e.g. more than 10%) to provide more efficacy and protection while still being smooth and stable in solution—which were not so far available in the market.
Oatmeal has been used throughout history as a topical application for the skin in cosmetic preparations, raw and for the bath. It has been used ground dry as well as cooked. Technology now allows the extraction of certain properties from the entire oat, not just the grain. Colloidal oatmeal, a product processed by grinding of the oat grain, has been consistently recommended for adults, geriatrics and infants in lotions, creams, shampoos, conditioners, soaps, ointments and the like as well as in bath and cleansing products. Oat derived colloidal oatmeal is devised for external application to the affected area of the body by applying directly to the desired area for treating skin discomforts as well as maintaining normal skin. Colloidal oatmeal additions to skin have a soothing effect on inflammation and irritation. Colloidal oatmeal is considered safe at all concentrations as an effective agent for symptomatic relief and treatment of dry skin and the resulting itching. Colloidal oatmeal, due to its physical and chemical properties, isolates exposed skin or mucous membrane surface from harmful or annoying stimuli and, thus, falls within the topical analgesic definition of skin protectant. Oatmeal leaves behind a thin occlusive film on the skin and this serves to hold in the adsorbed water. The result of this coating is that the skin is protected against irritation and hence the ingredient has an antipruritic and generally soothing effect.
However, colloidal materials for skin care preparations, as is the case of colloidal oatmeal, are not fully soluble in aqueous solutions and tend to leave undesirable residues on the skin and other surfaces. Furthermore, liquid oat extracts prepared by extraction with alcohol, glycols, ethers, esters and mixtures thereof are typically unstable materials, which, if not emulsified, readily separate into oil and aqueous phases which may further separate into soluble and insoluble phases. Alcohol soluble cereal proteins interact with a wide range of phenolic compounds naturally found in cereal grains, forming a chill haze or protein haze. These hazes will cause the extract to become turbid. Over time, the hazes will agglomerate resulting in an insoluble precipitate. Therefore, it is clear that it is very difficult to prepare a pharmaceutical or cosmetic compositions presenting high concentration of colloidal materials such as colloidal oatmeal without compromising its long-term stability, smooth feel and effectiveness.
Document U.S. Pat. No. 6,368,579B1 describes an “oat protein complex”, which comprises the colloidal oatmeal as the main active ingredient plus hydrolyzed oat protein and oat beta glucan extract as secondary active ingredients. According the aforementioned document, said complex would result in compositions presenting higher concentrations of colloidal oatmeal not often seen in other formulations, as they tend to get too thick. However, said stabilizer is different as compared to that of the present invention and the highest concentration of colloidal oatmeal presented in the formulations described in the examples of said document is 5.76% (w/w).
Patent documents US 2013/022562A1 and U.S. Pat. No. 6,416,788B1 describe formulations containing more than 40% (w/w) of colloidal oatmeal, but both are in dry loose powder form for bath dispersion purposes, not for direct application like a cream or ointment. This means that these formulations do not face the problems of stability that water-based or alcohol-based formulations do, which could not so far be stabilized if containing more than 1% (w/w) of colloidal oatmeal.
To best knowledge of the inventors, the problem of long term stability, smooth feel and effectiveness of higher concentrations of colloidal materials for skin care compositions—as is the case of colloidal oatmeal—has not been solved so far. In this context, the incorporation of more colloidal material such as oatmeal in semi-solid or “wet” pharmaceutical formulations without harming their stability and/or smooth feel is highly desirable and would increase the effectiveness of the formulation. This would also reduce the number of applications of the product through the day, thus, being extremely beneficial to the patients/users. The present invention solves these and other technical problems and further provides a direct topical formulation comprising more than 1% (w/w) of colloidal material, for skin care and/or treating skin disorders.